Methods for testing the performance of vehicle suspension systems are generally known.
Automotive vehicles commonly employ a suspension system connected between the road wheels and the body of the vehicle.
Conventional shock absorbers typically have a limited operating life, and therefore may need to be replaced when they no longer function properly. In order to determine if a shock absorber needs to be replaced, the simplest and most widely used conventional diagnostic testing approach typically involves a technician applying force to the vehicle fender, or elsewhere on the vehicle body, and visually detecting the rocking movement response of the vehicle. The resulting oscillations are often counted visually or by an oscillation measuring device attached to the vehicle. The conventional suspension testing approach therefore involves subjective interpretation by the technician which may not be consistently reliable.
As can be appreciated, this test cannot feasibly be applied to large vehicles such as road haulage trucks and the like.
Another test which may be applied is the European Drop Test, in which a set of axles is mounted on a test rig and is driven over an inclined ramp with a sheer drop of approximately 80 mm on its facing edge. The damping ratio and frequency of the suspension is then measured using load cells attached to the test rig.
The results gained in the above manners may be inaccurate and inconclusive in that they do not accurately take into account the combined effect of vehicle weight, suspension geometry and shock absorber characteristics as they relate to the efficiency of the shock absorber in maintaining the vehicle's wheel in contact with the road surface having regard to the road bumps which the vehicle normally encounters. Also these simple tests do not take into account multiple axles coupled together in what is commonly called a suspension group, for example, a tandem axle group, tri axle group, quad axle group, and the like.
Other known devices for testing shock absorbers test the dynamic reactions of suspension. Some of these devices require the removal of the shock absorbers from the vehicle. This practice is highly impractical for two reasons. First, labour costs involved in the shock absorber's removal for testing and subsequent reinstallation are prohibitive, in that such costs may be equal to or greater than the cost of replacement shock absorbers. This is particularly true with shock absorbers used in MacPherson-type suspensions wherein removal of the shock absorber necessitates the disassembly of other suspension components, such as the spring, balljoint and brake assembly.
Second, testing of a shock absorber isolated from its operating environment is believed to be unsatisfactory as its damping ratio is measured against an arbitrary standard rather than relative to the suspension system of which it is a part. As the performance of the shock absorber in conjunction with the rest of the suspension system affects the handling, ride, suspension performance, stability and safety of the vehicle, the practice of shock absorber testing as an isolated component can be seen to be unsatisfactory as a method of determining in-service performance of the suspension, or a suspension group as a whole unit in an operating environment.
As the shock absorber must be removed from the vehicle in order to test its performance using this test, the vehicle must be removed from service for the length of the tests. This results in a loss of profits for the owner operator while the vehicle cannot be used during the period of downtime.
Other devices currently on the market, namely those operating on the seismographic principle, evaluate the suspension systems as a whole, but are restricted to recording movement of the vehicle's body without allowing the determination of the damping ratio of the system, (i.e., shock absorber performance).
With the advent of the Intelligent Access Project (IAP) under the NRTC guidelines and with the future introduction of Performance Based Standards (PBS), haulage or freight trucks may be called upon to comply with these standards which relate to the performance of suspension and suspension components, as a whole or as a group of axles, so equipped. Under the IAP and the PBS guidelines, the vehicle suspension may be required to meet performance standards in order to maintain the compliance of the vehicle and its fitness for service. This compliance testing may test one or more parameters of the suspension which determine the “road friendliness” of the suspension. A “road friendly suspension” may be one which functions within predetermined limits for one or more of the parameters, and attaining or complying with “road friendliness” may provide advantages for the owner/operator of the vehicle such as the ability to carry heavier loads or access to roads which non-compliant vehicles may be restricted from using. As well, the road friendly performance of the suspension/s will affect the working life of the road itself with attendant reduction in maintenance costs and increased safety to all road users, with the economic benefits of such savings flowing on to the general community.
The compliance of the suspension is generally tested periodically over the life of the vehicle or of the vehicle suspension.
It is therefore desirable to provide for an accurate test procedure for testing the performance of suspension components on a vehicle to determine whether the suspension is functioning properly and within legally acceptable limits while the vehicle is in use and without requiring the removal of the vehicle from service. In addition, it is desirable to provide for a test procedure for testing vehicle suspension components that does not require subjective interpretation by a technician.